Rupert Murdoch’s 21st Century Fox is preparing a last-ditch push to seize control of media giant Sky as a final deadline for the £26 billion takeover battle looms.

The Mail on Sunday has learned that 21st Century Fox has hired an influential advisory firm to canvas support among Sky shareholders for its 1400p-a-share bid for the FTSE 100-listed broadcaster before its final throw of the dice.

The move has triggered speculation that the octogenarian media mogul – who has teamed up with Walt Disney, the US media giant in the process of buying most of 21st Century Fox from him – is poised to trump a rival offer by US cable group Comcast.

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A frenzied bidding war could break out with the approach of the September 22 deadline for final bids. Investors are braced for a fiery conclusion to the battle which has been raging for six months. So far Comcast has offered 1475p a share – beating Murdoch’s bid by 75p – and Sky’s board of independent directors has recommended that investors accept.

Georgeson is understood to have been asking Sky investors in recent days what they think of 21st Century Fox’s current offer and trying to gauge what would improve Murdoch and Disney’s chances of success.

Sky shares have recently been trading as high as 1540p as investors speculate that 21st Century Fox and Disney are considering a ‘knockout’ offer to scare off Comcast. The Takeover Panel, the respected City regulator, has told the two rival sides that if neither of their offers has been accepted by shareholders by the deadline it will hold a formal auction.

Octogenarian media mogul Rupert Murdoch

The suitors would then have an opportunity to submit revised offers in an orderly process managed by the Takeover Panel.

Disney – led by potential US Presidential candidate Bob Iger – and Comcast began battling for Murdoch’s 21st Century Fox assets last year. The main battle was won by Disney, which agreed to pay a massive $71 billion (£55 billion) for the majority of the assets including film and TV studios.As part of that deal, it is also in line to receive Fox’s 39 per cent stake in Sky.

Murdoch had separately made a bid to buy the remaining 61 per cent of Sky, potentially adding it to 21st Century Fox’s list of assets before the deal with Disney completes. Comcast launched a separate bid for Sky while attempting to buy 21st Century Fox.

Some of Sky’s largest shareholders have already said the business could be worth significantly more than Comcast’s 1475p a share offer. Crispin Odey, the colourful hedge fund manager, said earlier this summer that Sky could be worth as much as £50 billion – more than double what Comcast and 21st Century Fox have offered for the business.

Odey, who was once married to Murdoch’s daughter Prudence, owns around 0.61 per cent of Sky and is a long-term shareholder. Last June, Odey said: ‘Debt is so easy to serve and so cheap that they could easily be paying 1800p for Sky.

‘If your free cashflow looks like it’s going to come through at £2.5 billion, which it should do within a year, what are you willing to pay for that? Well, you’re willing to pay £50 billion – or around 2600p a share.’